ADCP测量悬沙浓度的可行性分析与现场标定

SUSPENDED SEDIMENT CONCENTRATION MEASUREMENTS WITH ADCP:FEASIBILITY ANALYSIS AND IN SITU CALIBRATION

根据现场观测数据 ,对ADCP测量悬沙浓度的进行标定实验。结果表明 ,在观测期间悬沙粒径变化较小的条件下 ,后散射强度与水样悬沙浓度之间存在较好的相关性。悬沙浓度剖面标定公式中的参数C′可用剖面实测水样浓度来确定 ,该参数与深度密切相关 :同一剖面不同深度之间有一定的波动 ,但同一深度不同潮时的变化很小。使用同一剖面参数C′的平均值计算出的剖面悬沙分布误差较大 (2 9%— 43% ) ,而按不同深度段分别标定 ,误差可以小于 2 0 % ,能够满足沉积动力学研究的需要。

For more than a decade,it has been recognized that the back scattered ADCP signal can be used to extract information on suspended objects. The present work,based on in situ measurements of suspended sediment concentrations by filtering of water samples and calculation of mean volume back scattering strength ( Sv ) of a 307.2kHz BBADCP,assesses the potential of ADCPs to measure the concentration quantitatively. Regression analysis shows that good correlation exists between the concentration (measured by filtration) and Sv ,and the mean relative error is less than 10%. These results suggest that the ADCP has the ability to measure the concentration under the condition that the grain size distribution of suspended material varies little during the survey period. An in situ calibration formula has been developed and used to calculate the suspended sediment concentration profile. The results indicate that the calibration parameter C′ varies with the depth,but its temporal variation is small at the same depth during a tidal cycle. Thus,the statistical error of concentration calculation associated with a profile averaged C′ value by the formula obtained ranges between 29% and 43%,and it becomes less than 20% when a time average value for different depths of the profile is used. The present study demonstrates the potential of ADCPs for direct measurement of suspended sediment concentration profiles.